(a) Field of the Invention
The present invention relates to a cathode ray tube (CRT) and, more particularly, to a CRT which can effectively enhance electron beam deflection efficiency.
(b) Description of the Related Art
Generally, CRTs include a panel having an inner phosphor screen, a funnel having a cone portion, and a neck having an electron gun therein, which are sequentially connected to each other. A deflection yoke is mounted around the cone portion of the funnel to form horizontal and vertical magnetic fields there. In this structure, electron beams emitted from the electron gun are deflected through the horizontal and vertical magnetic fields from the deflection yoke, and land on the phosphor screen.
Recently, the CRTs have been employed for the use in highly sophisticated electronic devices such as high definition television (HDTV) and OA equipment.
On the one hand, in these applications, the consumption power of the CRT should be reduced to obtain good energy efficiency, and the leakage magnetic field due to the power consumption should be reduced to protect the user from the harmful electronic waves. In order to cope with these requirements, it turns out that the consumption power of the deflection yoke, which is the major consumption source, should be reduced in a suitable manner.
On the other hand, in order to realize high brightness and resolution of display images on the screen, it is required that the deflection power of the deflection yoke should increase. Specifically speaking, higher anode voltage is required for enhancing brightness of the screen and, correspondingly, higher deflection voltage is required for deflecting the electron beams accelerated by the increased anode voltage. Furthermore, higher deflection frequency is required for enhancing resolution of the screen, accompanying with the requirement of increased deflection power. In addition, in order to realize relatively flat CRTs for more convenient use, wide-angle deflection should be performed with respect to the electron beams and this also accompanies with the requirement of increased deflection power.
In this situation, there are needs for developing techniques for allowing the CRTs to retain good deflection efficiency while constantly maintaining the deflection power or reducing it.
For this purpose, conventionally, a technique of increasing the deflection efficiency is introduced by positioning the deflection yoke to be more adjacent to the electron beam paths. The positioning of the deflection yoke is achieved by reducing a diameter of the neck and an outer diameter of the funnel adjacent to the neck. However, in such a structure, the electron beams to be applied onto the screen corner portions are liable to bombard the inner wall of the funnel adjacent to the neck (This phenomenon is usually called the xe2x80x9cbeam shadow neckxe2x80x9d or briefly the xe2x80x9cBSNxe2x80x9d). Consequently, the phosphors coated on the corresponding screen corner portions are not excited so that it becomes difficult to obtain good quality of screen images.
In order to solve such problems, it has been proposed that the cone portion of the funnel, around which the deflection yoke is mounted, should be formed with a shape where a circle gradually changes into a rectangle from a neck-side of the funnel to a panel-side. This shape corresponds to the deflection route of the electron beams. In this structure, the size of the cone portion is minimized so that the deflection yoke can be positioned to be more adjacent to the electron beam paths.
However, in the above technique, the cone portion of the funnel is merely designed to be formed with a rectangular shape without considering the practical moving routes of the electron beams in various directions, and thus does not cope with the beam shadow neck (BSN) in an appropriate manner.
It is an object of the present invention to provide a CRT which can effectively enhance electron beam deflection efficiency with appropriate structural components on the basis of the computer simulation technique.
This and other objects may be achieved by a CRT with a central axis. The CRT includes a panel with an inner phosphor screen and a rear portion. The panel has a substantially rectangular effective screen portion with two long sides in a horizontal axis direction, two short sides in a vertical axis direction and four edges in a diagonal axis direction. A funnel is connected to the rear portion of the panel. The funnel sequentially has a body with a large-sized end and a small-sized end, and a cone portion with a large-sized end and a small-sized end. The large-sized end of the body is sealed to the rear portion of the panel. The small-sized end of the body meets the large-sized end of the cone portion at a point. The meeting point of the body and the cone portion becomes an inflection point of the funnel. The cone portion has a sectional shape varying from a circle to a non-circle like a rectangle while proceeding from the small-sized end to the large-sized end such that the cone portion is provided with a curvature radius Rh in the horizontal axis direction, a curvature radius Rv in the vertical axis direction, and a curvature radius Rd in the diagonal axis direction. A neck is sealed to the small-sized end of the cone portion. An electron gun is fitted within the neck to produce electron beams. A deflection yoke is mounted around the cone portion of the funnel. The horizontal, vertical and diagonal curvature radii Rh, Rv and Rd of the cone portion of the funnel satisfy the following condition: Rh less than Rv less than Rd.
The cone portion of the funnel has an arc of circle with the horizontal curvature radius Rh, an arc of circle with the vertical curvature radius Rv, and an arc of circle with the diagonal curvature radius Rd. The arcs of circle with the horizontal, vertical and diagonal curvature radii Rh, Rv and Rd each have a center positioned toward the neck with respect to the small-sized end of the cone portion in the tube axis direction. The distance between the small-sized end of the cone portion and each center of the arcs of circle with the horizontal, vertical and diagonal curvature radii Rh, Rv and Rd is sequentially reduced.
Furthermore, the arcs of circle with the horizontal, vertical and diagonal curvature radii Rh, Rv and Rd have centers positioned toward an outer surface of the funnel with respect to the tube axis in the horizontal, vertical and diagonal axis directions, respectively. The distance between the tube axis and each center of the arcs of circle with the horizontal, vertical and diagonal curvature radii Rh, Rv and Rd sequentially increases.